There are two kinds of linear actuator cylinders. The first kind is the conventional combination of the stationary cylinder and moving piston with connecting rod extending through one end wall of the cylinder. The second kind is the actuator known as the "rodless actuator cylinder" comprising a connecting member disposed adjacent to the cylindrical side of the cylinder that reciprocates following the cylindrical wall of the cylinder. While there are a number of different designs and constructions for the existing "rodless cylinders", none of the existing versions is capable of operating on a high pressure source such as an ultra-high pneumatic pressure source or hydraulic pressure source and of delivering a high power actuation with structural rigidity and strength.